Displays take many different configurations. In many displays (e.g., flat panel displays, field emission displays) it is required that photoresist be deposited on surfaces having structures projecting therefrom, e.g., spacers on a face plate surface of a flat panel display. Such structures projecting from the surfaces reduce the effectiveness of conventional photoresist application methods used in the formation of features on the surfaces, e.g., photoresist used for patterning phosphors on face plate surfaces.
For example, as described in U.S. Pat. No. 5,486,126, entitled "Spacers For Large Area Displays," issued Jan. 23, 1996, and assigned to Micron Display Technology, Inc., flat panel displays include a cathode emitting structure and a corresponding anode display structure for use in displaying one or more color images on the display. In such field emission devices, there is a relatively high voltage differential between the cathode emitting structure (also referred to as base electrode, base plate, emitter surface, cathode surface, etc.) and the anode display structure (also referred to as an anode, cathodoluminescent screen, display screen, face plate, or display electrode). As indicated in U.S. Pat. No. 5,486,126, it is important that electrical breakdown between the electron cathode emitting structure, i.e., base plate, and the anode display structure, i.e., face plate, be prevented. At the same time, however, narrow spacing between the base plate and face plate is necessary to maintain a desired structurally thin display and to obtain high image resolution. To provide for such narrow spacing, it is required that various features, e.g., spacers, exist between the base plate and face plate of the display.
Spacers incorporated between the display face plate and base plate have certain characteristics. For example, such spacer structures are generally nonconductive to prevent electrical breakdown between the face plate and base plate in spite of the relatively close spacing therebetween and relatively high voltage differential, e.g., 300 or more volts. However, such spacer structures may have portions that are conductive.
The spacers may include pillars as described in U.S. Pat. No. 5,486,126; support structure as described in U.S. Pat. No. 5,667,418 entitled "Method Of Fabricating Flat Panel Device Having Internal Support Structure," issued Sep. 16, 1997; spacer structure as described in U.S. Pat. No. 5,675,212 entitled "Spacer Structure For Use In Flat Panel Displays And Methods For Forming Same," issued Oct. 7, 1997; spacers as described in U.S. Pat. No. 5,634,585 entitled "Method For Aligning And Assembling Spaced Components," issued Jun. 3, 1997; U.S. Pat. No. 5,503,582 entitled "Method For Forming Spacers For Display Devices Employing Reduced Pressures," issued Apr. 2, 1996; U.S. Pat. No. 5,232,549 entitled "Spacers For Field Emission Display Fabricated Via Self-Aligned High Energy Ablation," issued Aug. 3, 1993; and U.S. Pat. No. 5,205,770 entitled "Method To Form High Aspect Ratio Supports (Spacers) For Field Emission Display Using Micro-saw Technology," issued Apr. 27, 1993; or any other spacer configuration, such as a screen printed feature, a stencil printed feature, glass spheres, etc.
Such spacers are fixed in one manner or another to either the face plate or the base plate. In many circumstances, such as when processes involved in making the base plate prevent the adhesion of spacers thereto or when such processes may weaken or damage the spacers, it is required that such spacers be attached or otherwise affixed to the face plate. Further, when the light emitting material, e.g., phosphors, impedes the adhesion of the spacers to the face plate, the spacers must be attached to the face plate prior to the phosphors being formed thereon. For example, U.S. Pat. No. 5,486,126 describes a method of disposing micropillar spacers on a surface of the face plate of a display.
Phosphors deposited on the surface of the face plate emit energy when excited by electrons. Phosphors are normally composed of inorganic luminescent materials that absorb incident radiation and subsequently emit radiation within the visible region of the spectrum. Phosphors are preferably capable of maintaining luminescence (e.g., fluorescence) under excitation for a relatively long period of time to provide superior image reproduction. Various phosphors include, for example, Y.sub.2 O.sub.3 :Eu, ZnS:Ag, Zn.sub.2 SiO.sub.4 :Mn, ZnO:Zn, or other doped rare earth metal oxides.
Affixation of the spacers to the face plate structure of a display prior to deposition of phosphors thereon presents problems in the deposition and patterning of such phosphors. Such problems result at least in part from the lack of ability to provide a uniform layer of patternable material in the regions between the spacers and, in particular, in areas directly adjacent to the spacers. A uniform layer of patternable material is necessary so that photolithographic processes can be effectively performed, as is done using phosphor slurries to make CRT screens, e.g., as described in U.S. Pat. No. 3,387,975 entitled "Method Of Making Color Screen Of A Cathode Ray Tube," issued Mar. 10, 1965.
For example, if the face plate having the spacers projecting therefrom is coated with a patternable material, e.g., resist, by spin coating, areas of noncoating or minimal coating may occur on the face plate adjacent the spacers as a result of such spacers blocking the flow of the patternable material. The patternable material also tends to form a meniscus with the spacers, resulting in a layer that is generally too thick and very non-uniform, particularly in regions adjacent to the spacers. Similar problems occur with meniscus, dip, or spray coating techniques.
Electrophoretic photoresist technology has been described in various articles and patents. For example, the article by D.A. Vidusek, entitled "Electrophoretic Photoresist Technology: An Image of the Future--Today," presented in December 1988 at the EIPC Winter Conference in Zurich, Switzerland, describes electrophoresis as a new technique for applying photoresist. Further, such electrophoretic deposition processes and photoresist for use in such processes are described in U.S. Pat. No. 4,592,816, entitled "Electrophoretic Deposition Process," issued Jun. 3, 1986; U.S. Pat. No. 4,751,172, entitled "Process For Forming Metal Images," issued Jun. 14, 1988; U.S. Pat. No. 5,004,672, entitled "Electrophoretic Method for Applying Photoresist to Three-Dimensional Circuit Board Substrate," issued Apr. 2, 1991; U.S. Pat. No. 5,196,098, entitled "Apparatus and Process for Electrophoretic Deposition," issued Mar. 23, 1993; and U.S. Pat. No. 5,607,818 entitled "Method For Making Interconnects And Semiconductor Structures Using Electrophoretic Photoresist Deposition," issued Mar. 4, 1997.